Molybdenum disilicide is attractive for high temperature applications because of their strength, oxidation resistance (at most temperatures), and relatively low cost. It's commonly used as heating elements. It's high temperature properties also make it potentially useful in aerospace applications such as gas turbines, particularly as the gas turbine industry strives toward higher engine outputs and efficiencies through designs that operate at higher temperatures and stresses.
The current material family of choice for high temperature applications in gas turbine engines is the superalloy family. Molybdenum disilicide offers potential advantages compared to superalloys, including lower density and potentially higher use temperatures.
A significant limitation encountered by the prior art on the use of molybdenum disilicide has been pesting. Pesting is the rapid oxidation of the material at intermediate temperatures of about 300.degree.-600.degree. C., and is particularly rapid at about 500.degree. C. It is believed that pesting occurs when molybdenum oxides such as MoO.sub.3 form within microcracks in the material. As these oxides grow in volume, they mechanically wedge the cracks apart and eventually cause fracture.
Raj, in U.S. Pat. No. 5,330,590 discusses this phenomena and concludes that molybdenum disilicides are not suited for aircraft engine component applications.
U.S. Pats. Nos. 5,292,691, 5,292,692, and 5,308,806, issued to Maloney et al, disclose molybdenum disilicide composite materials and methods of manufacture. The references teach that composites may be produced from commercially available molybdenum disilicide powders reinforced by metallic or semi-metallic fibers for increased strength, creep resistance, and toughness.
Molybdenum disilicide materials possess a number of useful properties and it is desired to use them in high temperature applications. It is also desired that they be produced at relatively low cost.
It is therefore the object of the present invention to provide a molybdenum disilicide material that does not experience pesting.
Another object of the invention is to provide a relatively low cost molybdenum disilicide material.
Yet another object is to provide a pest resistant coating material based on MoSi.sub.2.